Experimental Data Snapshot

  • Resolution: 1.90 Å
  • R-Value Free: 0.236 
  • R-Value Work: 0.182 
  • R-Value Observed: 0.182 

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Crystal structure of Y34F mutant human mitochondrial manganese superoxide dismutase and the functional role of tyrosine 34.

Guan, Y.Hickey, M.J.Borgstahl, G.E.Hallewell, R.A.Lepock, J.R.O'Connor, D.Hsieh, Y.Nick, H.S.Silverman, D.N.Tainer, J.A.

(1998) Biochemistry 37: 4722-4730

  • DOI: https://doi.org/10.1021/bi972394l
  • Primary Citation of Related Structures:  
    1AP5, 1AP6

  • PubMed Abstract: 

    Tyrosine 34 is a prominent and conserved residue in the active site of the manganese superoxide dismutases in organisms from bacteria to man. We have prepared the mutant containing the replacement Tyr 34 --> Phe (Y34F) in human manganese superoxide dismutase (hMnSOD) and crystallized it in two different crystal forms, orthorhombic and hexagonal. Crystal structures of hMnSOD Y34F have been solved to 1.9 A resolution in a hexagonal crystal form, denoted as Y34Fhex, and to 2.2 A resolution in an orthorhombic crystal form, denoted as Y34Fortho. Both crystal forms give structures that are closely superimposable with that of wild-type hMnSOD, with the phenyl rings of Tyr 34 in the wild type and Phe 34 in the mutant very similar in orientation. Therefore, in Y34F, a hydrogen-bonded relay that links the metal-bound hydroxyl to ordered solvent (Mn-OH to Gln 143 to Tyr 34 to H2O to His 30) is broken. Surprisingly, the loss of the Tyr 34 hydrogen bonds resulted in large increases in stability (measured by Tm), suggesting that the Tyr 34 hydroxyl does not play a role in stabilizing active-site architecture. The functional role of the side chain hydroxyl of Tyr 34 can be evaluated by comparison of the Y34F mutant with the wild-type hMnSOD. Both wild-type and Y34F had kcat/Km near 10(9) M-1 s-1, close to diffusion-controlled; however, Y34F showed kcat for maximal catalysis smaller by 10-fold than the wild type. In addition, the mutant Y34F was more susceptible to product inhibition by peroxide than the wild-type enzyme. This activity profile and the breaking of the hydrogen-bonding chain at the active site caused by the replacement Tyr 34 --> Phe suggest that Tyr 34 is a proton donor for O2* - reduction to H2O2 or is involved indirectly by orienting solvent or other residues for proton transfer. Up to 100 mM buffers in solution failed to enhance catalysis by either Y34F or the wild-type hMnSOD, suggesting that protonation from solution cannot enhance the release of the inhibiting bound peroxide ion, likely reflecting the enclosure of the active site by conserved residues as shown by the X-ray structures. The increased thermostability of the mutant Y34F and equal diffusion-controlled activity of Y34F and wild-type enzymes with normal superoxide levels suggest that evolutionary conservation of active-site residues in metalloenzymes reflects constraints from extreme rather than average cellular conditions. This new hypothesis that extreme rather than normal substrate concentrations are a powerful constraint on residue conservation may apply most strongly to enzyme defenses where the ability to meet extreme conditions directly affects cell survival.

  • Organizational Affiliation

    Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
198Homo sapiensMutation(s): 1 
UniProt & NIH Common Fund Data Resources
Find proteins for P04179 (Homo sapiens)
Explore P04179 
Go to UniProtKB:  P04179
PHAROS:  P04179
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP04179
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on MN

Download Ideal Coordinates CCD File 
C [auth A],
D [auth B]
Experimental Data & Validation

Experimental Data

  • Resolution: 1.90 Å
  • R-Value Free: 0.236 
  • R-Value Work: 0.182 
  • R-Value Observed: 0.182 
  • Space Group: P 61 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 80.9α = 90
b = 80.9β = 90
c = 242.5γ = 120
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1998-01-28
    Type: Initial release
  • Version 1.1: 2008-03-03
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Derived calculations, Version format compliance
  • Version 1.3: 2021-11-03
    Changes: Database references, Derived calculations
  • Version 1.4: 2023-08-02
    Changes: Refinement description